This invention relates to a switched power regulator having improved power factor correction apparatus.
Various power supply systems are known which incorporate a switched power regulator, such as the boost converter, the buck converter and the buck-boost converter. A problem with these conventional converters is that they do not provide inherent power factor correction. Adding the capability of power factor correction increases the size, complexity and cost of these devices.
One known type of converter is the current programmed DC boost converter operating in the discontinuous conduction mode, as is shown in FIG. 1, and which will be discussed in greater detail below. This converter generates a control signal (V.sub.M) for regulating the average value of the output voltage, V.sub.out, while providing power factor correction such that the converter draws a sinusoidal current from the input lines, for example, the 120 volt AC/60 Hz power lines commonly available. The control voltage V.sub.M generated therein satisfies the following expression ##EQU1## and produces a near unity power factor apparatus. In the foregoing expression, L is the inductance of the series inductor, i.sub.in is the maximum amplitude of the input current to the boost converter, V.sub.in is the maximum amplitude of the converter input voltage and V.sub.out is the regulated output voltage thereof. A disadvantage of this apparatus is that its control circuit with power factor correction is rather complicated since it requires an adder (substractor) circuit, a multiplier, a square root generator and a fixed ramp sawtooth generator. Another drawback is that it does not inherently provide over current protection for the transistor switch, especially in the case of a voltage transient from the 120 volt AC input lines, because it does not provide control of the switch current on a pulse by pulse basis.
Additional background information on switching regulator circuits can be obtained from U.S. Pat. No. 4,311,954 (1/19/82) and U.S. Pat. No. 4,471,291 (9/11/84).